Yambol (Bulgarian: Ямбол [ˈjamboɫ]) is a city in Southeastern Bulgaria and administrative centre of Yambol Province. It lies on both banks of the Tundzha river in the historical region of Thrace. It is occasionally spelled Jambol.

Yambol is the administrative center of two municipalities. One is Yambol Municipality, which covers the city itself, and the other is Tundzha Municipality, which covers the rural areas around Yambol.

The area surrounding Yambol has been inhabited since the Neolithic Era. The ancient Thracian royal city of Kabile or Kabyle (Bulgarian: Кабиле), dating from the end of the 2nd millennium BCE, was located 10 km from current-day Yambol. It was one of Thracians' most important cities and contained one of the kings' palaces. The city was conquered by King Philip II of Macedon in 341 BCE and was re-established as an Ancient Greek polis. After the collapse of Alexander the Great’s empire in the 3rd century BCE, Kabile was ruled by the Thracians once again. It was conquered by the Romans in 71 BCE and later incorporated into the Roman province of Thrace. By 136 CE, Kabile was one of the largest Roman military bases in the region housing at least 600 soldiers. A large residence for military officers has recently been excavated in the archaeological park at Kabile.

Kabile was expanded by Roman Emperor Diocletian in 293 CE. Although it was named Diospolis (Διόςπόλις in Greek 'city of Zeus'), the name also reflected the first syllable of emperor Diocletian's name. The name later evolved through Diampolis (Διάμπόλις), Eiambouli (Ηιάμβόυλι; in Byzantine chronicles), Dinibouli (دنبلي; Arabic chronicles), Dbilin (Дбилин; in Bulgarian inscriptions), and Diamboli or Jamboli (Диамбоюли) to become Yambol. Prior to the 1945 spelling reform, the name was rendered with an additional yer at the end, as Ямболъ.

Kabile was conquered by the Goths in the 4th century CE and was destroyed by the Avars in 583. As the Slavs and Bulgars arrived in the Balkans in the Middle Ages, the Kabile fortress was contested by the First Bulgarian Empire and the Eastern Roman Empire. It ultimately became part of Bulgaria in 705 CE during the reign of Khan Tervel and has been an important Bulgarian center ever since.

The city expanded during the reign of Khan Omurtag of the First Bulgarian Empire, and a new fortress was built. Its proximity to the border made it essential for both trade and military purposes. During the reign of Boris I and Tsar Simeon, the first literary centers were established, mostly as part of the church. Books were imported from Preslav and Ohrid literary schools and were studied in the city's churches.

During the reign of Tsar Kaloyan, the city again increased in importance, mainly due to the ongoing conflict between Bulgaria and the crusaders. A major battle between Tsar Kaloyan and the crusaders happened in 1204 CE, about 80 kilometers south-west of the town, where Bulgaria defeated the crusaders in the battle of Adrianopole on 14 April 1205.

The Ottoman Turks conquered Yambol in 1373 CE, but a militarized, semi-independent Bulgarian population remained as voyinuks in the southern part of the city. It was renamed to "Yanbolu" in Turkish. It was a kaza center of the Ottoman Empire, which was bound successively to Çirmen Sanjak (Its center was Edirne) of Rumelia Eyalet (1364–1420), Silistre Sanjak of Rumelia Eyalet (1420-1593), Silistre Sanjak of Silistre Eyalet (1593–1830), İslimye Sanjak of Edirne Vilayet (1830–1878), and the department of Sliven in Eastern Rumelia before joining the Principality of Bulgaria in 1885.